1. Field of the Invention
The present invention relates to recyclable, rigid, plastic, packaging containers which are highly resistant to gas permeation and water vapor transmission. The containers may be made in the form of pipes, bottles, barrels, tubs, cans, trays and the like. They are formed by means of blow molding, injection blow molding, and injection molding techniques.
2. Description of the Prior Art
Rigid plastic containers are finding an ever increasing use in packaging articles of commerce. In particular, the field of food and beverage packaging in plastics is increasing at a very rapid rate. Food products such as milk, syrups, fruit juices, instant coffee and tea, peanut butter, margarine, mayonnaise, dips, prepared salads, condiments and other food products are found on today's grocery shelves in rigid plastic containers. Rigid plastic containers also find wide use in the packaging of cosmetics, such as skin lotions, shampoos, ointments, etc., and in the pharmaceutical field are used for packaging many drugs.
In oder to provide a suitable package for the many commodities purchased by the general public, a plastic container must have the requisite rigidity, strength and impermeability. The container must be sufficiently rigid to be handled on conventional high speed filling and capping lines and to be handled during shipment and by the ultimate consumer during use. The plastic container must also be sufficiently strong to contain the product, particularly if the product is under pressure as in the case of carbonated beverages. Strength is also an important factor in that the container should be resistant to breakage during filling, transporting and use by the consumer. Impermeability to fluids (water, oxygen, carbon dioxide, etc.) is important for packaging of foods and carbonated beverages. In order to achieve widespread commercial acceptance, a plastic container must be inexpensive, be attractive in appearance, and be capable of manufacture by conventional high speed plastic container manufacturing equipment, in particular, by blow molding, injection blow molding or injection molding. A third and ever increasingly important requirement for a plastic container is that it be ecologically acceptable.
As a practical matter, plastic containers presently in use do not meet all the criteria found above. Many containers have the required rigidity and strength and are inexpensive, such as those made from high and low density polyethylene, polyvinyl chloride and oriented polypropylene. However, these containers do not provide the desired impermeability which is required in packaging many products, e.g., carbon dioxide-containing beverages, oxygen-sensitive foods, etc. On the other hand, plastic materials having the requisite impermeability properties, e.g., polyvinylidene chloride polymers, nitrile-containing polymers, are relatively expensive or cannot be readily fabricated into containers by extrusion-based methods or do not possess the necessary strength or desirable optical properties, such as high impact strength, creep resistance, transparency, or the like.
In order to overcome the deficient properties of the individual thermoplastic materials, the prior art has taught the desirability of producing a blow molded container by coextruding two different plastic materials, each having certain desired properties, to form a composite parison and then blow molding this parison in a hollow blow mold to produce small-neck containers. See U.S. Pat. No. 2,710,987. In order to overcome some of the strength deficiencies in blow molded plastic containers, U.S. Pat. No. 3,140,004 describes the fabrication of a blow molded, multilayer, plastic container utilizing two plastic materials having different coefficients of thermal contraction. U.S. Pat. No. 3,082,484 describes a method of forming a container wherein one of the thermoplastics used has such a low viscosity that it cannot be extruded into a parison for blow molding. Nylon, which normally cannot be blow molded alone, is encased in a polyethylene jacket to produce a container having the desirable characteristics of both nylon and polyethylene. French Patent No. 1,423,666 describes the preparation of blow molded plastic containers from two or more plastic materials by coextruding a parison having one layer of a vinyl halide polymer or copolymer, or an olefinic polymer, and the other layer of a vinylidene chloride polymer. According to U.S. Pat. No. 3,449,479, a preformed parison of a polyolefin is coated with a chlorine-containing polymer, e.g., polyvinyl chloride, polyvinylidene chloride-acrylonitrile copolymers, by solution or powder coating techniques. The coated parison is then oriented and converted into a bottle in a blow molding operation.
Methods for producing multilayered plastic containers by plastic forming techniques other than blow molding, injection molding and injection blow molding are disclosed in British Patent No. 1,238,577 and Netherlands Application No. 71/15611. In the British patent, a laminated sheet composed of a load-carrying lamina and a fluid-barrier lamina is subjected to a compression forming operation. The method of the Netherlands application involves thermoforming a multilayer, laminated sheet of plastic material, one lamina of which is a high barrier thermoplastic such as Rarex 210, the other being polystyrene.
While many combinations of materials and processes for producing multilayer plastic containers have been suggested heretofore, these containers have not found significant acceptance commercially in large volume applications. One of the primary reasons is believed to be excessive production costs. For example, in most blow molding machines used commercially today, waste neck and tail scrap is produced in significant quantities. The scrap presents no problem when bottles are made from a single-layer parison, since the neck and tail scrap portions can be reground and recycled into the thermoplastic feed material. However, as far as is known heretofore there has been no commercially feasible way to recycle the tail or neck scrap produced when blow molding multilayer bottles. Since most of the multilayer bottles are made from parisons in which the two or more layers are strongly bonded, these thermoplastic materials cannot be separated for refeeding to the respective resin feeds. See, for example, U.S. Pat. No. 3,449,479. Attempts to feed multilayer scrap regrind have been unsuccessful in that the most commonly used barrier resins are incompatible with the other thermoplastic resins used for the load-bearing lamina, resulting in bottles which are hazy, weak and commercially unacceptable.
From an ecological standpoint the multilayer bottles produced by the processes taught in the prior art are not suitable for recycling to produce recovered resin for reuse in producing bottles. Because the problem of separating the barrier layer from the load-bearing layer has not been heretofore solved, there has been no economic incentive to return multilayer plastic bottles to separation centers for recovery of the plastic materials therein for reprocessing into new plastic bottles.